Tensions were already high after Vice President Tareck El Aissami made an unannounced morning visit to the National Assembly, accompanied by top government and military officials, for an event celebrating independence day.

The short appearance at the congress by top officials who have repeatedly dismissed the legislators as a band of U.S.-backed conspirators was seen by many as a provocation.

El Aissami said global powers are once again trying to subjugate Venezuela. "We still haven't finished definitively breaking the chains of the empire," he said, adding that President Nicolas Maduro's plans to rewrite the constitution — a move the opposition sees as a power-grab — offers Venezuela the best chance to be truly independent.

— Juan Barreto / AFP - Getty Images

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Female soldiers march during a military parade marking 206 years of Venezuela's declaration of independence from Spain.

— Ariana Cubillos / AP

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After El Aissami left, dozens of government supporters set up a picket outside the building, heckling lawmakers with menacing chants.

Pro-government militias beat Deputy Armando Armas."This doesn't hurt as much as watching how every day how we lose a little bit more of our country," Arias said from inside an ambulance as he was being treated for head wounds that spilled blood across his clothes.

— Miguel Gutierrez / EPA

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Deputy Americo De Grazia, center, is beaten by protesters outside the National Assembly.

— Miguel Gutierrez / EPA

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De Grazia is led away by bodyguards.

— Fernando Llano / AP

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De Grazia lies on an infirmary bed before being taken in a stretcher to an ambulance. He suffered from convulsions, said a fellow congressman.